The molecular and crystal structure of an acetonitrile solvate of the synthetic, terminally-blocked homo-tetrapeptide from alpha-aminoisobutyric acid [Ac-(Aib)4-OtBu] (1) was determined by single-crystal X-ray diffraction. The compound possesses the following parameters: triclinic, space group P1BAR (No. 2), a = 17.751(2) angstrom, b = 9.999(2) angstrom, c = 9.327(2) angstrom, alpha = 11 3.0(1)-degrees, beta = 85.6(1)-degrees, gamma = 105.0(1)-degrees, and Z = 2. The crystal structure was solved by direct methods. The least-squares refinement led to R and R(w) values of 0.059 and 0.061, respectively, for 3472 reflections with I greater-than-or-equal-to 3-sigma(I). The tetrapeptide is folded into two consecutive type-III (III') beta-bend conformations (incipient 3(10)-helix), stabilized by two intramolecular N-H...O = C H-bonds. A short contact is observed between the nitrogen atom of the acetonitrile molecule and the Aib2 NH group.
Linear Oligopeptides .253. Molecular and Crystal-structure of A Terminally-blocked Aib Homotetrapeptide
FORMAGGIO, FERNANDO;TONIOLO, CLAUDIO
1992
Abstract
The molecular and crystal structure of an acetonitrile solvate of the synthetic, terminally-blocked homo-tetrapeptide from alpha-aminoisobutyric acid [Ac-(Aib)4-OtBu] (1) was determined by single-crystal X-ray diffraction. The compound possesses the following parameters: triclinic, space group P1BAR (No. 2), a = 17.751(2) angstrom, b = 9.999(2) angstrom, c = 9.327(2) angstrom, alpha = 11 3.0(1)-degrees, beta = 85.6(1)-degrees, gamma = 105.0(1)-degrees, and Z = 2. The crystal structure was solved by direct methods. The least-squares refinement led to R and R(w) values of 0.059 and 0.061, respectively, for 3472 reflections with I greater-than-or-equal-to 3-sigma(I). The tetrapeptide is folded into two consecutive type-III (III') beta-bend conformations (incipient 3(10)-helix), stabilized by two intramolecular N-H...O = C H-bonds. A short contact is observed between the nitrogen atom of the acetonitrile molecule and the Aib2 NH group.Pubblicazioni consigliate
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